The present invention generally relates to temperature control systems for maintaining the temperature of an electronic device at a predetermined temperature while the device is being tested.
Testing equipment has been utilized in the electronics industry to test the operation of integrated circuits and other electronic devices maintained at a predetermined temperature. Generally, the testing equipment will include a thermal head having a temperature controlled surface for contacting the electronic device being tested. The thermal head is simultaneously heated and cooled in an attempt to maintain the predetermined temperature. The test equipment users (i.e., electronic device manufacturers) generally specify that the thermal head be capable of maintaining the predetermined temperature under all conditions with a variance of ±3° C.
With some such testing equipment, the predetermined temperature can be varied at the option of the technician conducting the testing procedure. Thus, electronic devices can be tested at multiple temperatures to simulate a wide variety of operating conditions. In order to produce the desired temperature at the thermal head, these devices have circulated a chilled liquid, such as water or ethylene glycol, through the thermal head. The liquid itself is chilled in a heat exchanger including the evaporator of a separate refrigeration system. In other words, the evaporator is cooled by the refrigeration system, which then serves to chill the circulating liquid. Heat may be added by heating elements incorporated into the thermal head when necessary to maintain the predetermined temperature.
This prior art technique of using a separate liquid loop presents a number of significant disadvantages. For example, additional maintenance requirements are contributed by the presence of the liquid loop. Moreover, the entire “cool side” of the liquid loop will often be below dew point, thus requiring extensive insulation. Often, it takes systems utilizing a liquid loop up to an hour to reach the desired temperature before testing can begin. The liquid loop also increases the size and power consumption requirements of the testing system.